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The intermittent nature of solar energy requires integration of an energy storage system with solar collector devices in order to have un-interrupted supply of energy in the absence of the availability of solar energy. The use of Phase Change Material (PCM) and rock bed for heat storage has been studied in the past decades. However, limited knowledge exists on the use of the combination of PCM and rock particles for high temperature heat storage with air as the medium of heat transfer. The aim of this paper is to show experimentally by means of comparison, the thermal behaviours of thermal energy storage with only rocks and that with rocks and PCM. A heat storage consisting of only rocks and that with rocks and PCM has been designed and built. The PCM material used is a mixture of NaNO3 and KNO3 in the ratio of 60:40 percent (mol%). The charging and thermal de-stratification profiles were investigated for both cases. The results showed that the introduction of PCM cylinders in a bed of rocks for heat storage does not only increase the energy content of the storage but it also increases the vertical thermal conductivity. The increase in vertical thermal conductivity is attributed to the high thermal conductivity of the PCM container material.

Solid state fermentation (SSF) which involves the growth of microorganism on moist solid substrates in the absence of free flowing water, has gained renewed attention over submerged fermentation for specific applications. During the SSF process in fermenter, there are three main engineering problems encountered such as the removal of metabolic heat from the substrate, diffusion of O2 and moisture through the substrate, and heterogeneity of the substrate and inoculum. A fluidized bed fermenter in which the particles move independently like a fluid was proposed to conduct the study. Throughout the study, rapid heat transfer from PKC to air was experimentally observed within the first 150 s with a temperature drop of 30 °C. This indicated that the excellent heat transfer between palm kernel cake and air allows solid state fermentation of PKC without accumulation of metabolic heat in the fermenter. Apart from heat removal, water adsorption study on PKC from air to bed was carried out. It showed that the increase of adsorbed water in PKC was proportional to air relative humidity and inversely proportional to superficial air velocity. The maximum moisture content adsorbed by PKC under fluidization conditions was around 10% (on dry basis). Finally, mathematical models for heat and mass transfer were proposed which can predict the experimental data quite satisfactorily.